This application claims the priority of German Patent Application, Ser. No. 199 305 37.4, filed Jun. 28, 1999, the subject matter of which is incorporated herein by reference.
The present invention relates to a telescopic crane of a type having a substructure, a revolving superstructure mounted to the substructure, a counterweight and a boom structure comprised of a main boom having a boom base and at least one telescope section which is received in the boom base and displaceable between retracted and extended positions.
In extended position, telescopic cranes are exposed to varying degrees of stress depending on the angular disposition. Oftentimes, the lateral deformation of the main boom in steep-incline disposition is the criterion that limits the load-carrying capability. When the angular disposition is flat or average, the loads applied in the mounting of the extended telescope sections represent a crucial criterion for the maximum load-carrying capability. In the latter case, the so-called super lift operation has been developed for torque relief.
The use of telescopic cranes with super lift operation has been known for a long time. An example is illustrated in a brochure issued by Mannesmann Demag Fordertechnik, Demag AX 1600, April 1996, pages 5, 17 and 27. A guy truss is arranged on the boom base of the main boom for placement on the boom base to increase the load-carrying capability and to reduce sag of the main boom. The guy truss is connected, on the one hand, to the foot region of the main boom via a guy rope of substantially constant length, and, on the other hand, to the head or collar of one of the inner telescope sections via a further guy rope of normally variable length. This reinforcing configuration is applicable for the base unit alone, or in conjunction with the arrangement of a fly jib in the form of a latticed tower which can be of the fixed type or luffing type. Telescopic cranes of this kind suffer shortcomings because the boom structure deforms laterally, especially in steep-incline disposition.
It is thus an object of the present invention to provide an improved telescopic crane, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved telescopic crane whose lateral deformation of the boom structure is significantly reduced, in particular in steep-incline disposition, compared to conventional telescopic cranes.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing at least one guy support which is mounted to the boom structure and connected to a tension means extending substantially longitudinally in the direction of the boom structure, with the guy support oriented with respect to the luffing plane at an inclination which is so selected that a lateral load acting on the boom structure is partially or entirely received by the guying.
The inclination of the guy support can be realized transversely to the longitudinal direction or in longitudinal direction or in superimposed transversely to and longitudinally in direction of the boom structure.
According to another feature of the present invention, two inclined guy supports can be provided on the topside of the respective boom element of the boom structure, whereby the angular disposition of both guy supports is normally identical. Of course, the angular disposition of both guy supports may also differ depending on the direction of the forces acting on the boom structure. The foot ends of both guy supports may be connected to the topside of the boom structure at a common area, or may be offset to one another. It is also conceivable to connect the foot end of at least one of the guy supports with the boom structure in the transition zone between topside and respective sidewall. As an alternative, there is also the option to arrange the foot end of at least one of the guy supports upon a girder which extends transversely to the longitudinal axis of the boom structure and projects beyond the boom structure.
Through the provision of a guy support according to the present invention, the portion of the guying force, effective in lateral direction, can be gradually and continuously modified in dependence on the angular disposition of the guy support. In the event, two guy supports are arranged offset to one another, both parallel guy supports act as super lift operation in a same manner as the conventional guy truss, when the boom structure is in the one extreme disposition, i.e. vertical disposition. At an angular position of  less than 90xc2x0 to  greater than 0xc2x0 for both guy supports, the effective tautening force is split into a component super lift operation and a component lateral guying. In the other extreme position, i.e. horizontal disposition, both guy supports realize a reinforcement in both lateral directions.
The free head end of each guy support can be selectively connected via a first tension member with the substructure, the superstructure, the foot region of the boom structure, the fixed or separately guided counterweight, or the bottom in the direction of the boom structure, and via a further tension member with a selected area of the boom structure in the direction of its head. The respectively desired angular disposition of the guy supports may be adjusted step-by-step or continuously by swinging the guy supports, so that an asymmetric angular disposition is also possible. Thus, when a lateral force is applied on one side, the respective guy support is inclined progressively in the direction of lateral guying whereas the other guy support remains in a central disposition.
As the distance of the tension members from the boom structure has also an impact on the desired reinforcement, it is proposed to change the length of the guy supports in steps or continuously. The tension members may be a guy rope or a guy rod, and may be arranged with or without prestress. When prestressed at a degree that can be re-adjusted, the tension means is operatively connected with a tensioning mechanism. Suitably, the tensioning mechanism is a winch or a piston and cylinder unit. However, it is also possible, to exploit the angular disposition and/or change in length of the guy supports as tensioning mechanism. The tensioning mechanism may be selectively mounted to the guy supports, to the boom structure, to the superstructure or substructure, or to the counterweight.
According to another feature of the present invention, the guy supports are mounted to the main boom in the area of the boom base, in particular in the forward region between the hinged attachment of the luffing cylinder and the forward bearing on the boom base. Each guy support is suitably connected to a piston and cylinder unit which is mounted to the boom base, for continuous adjustment of the guy supports.
According to another feature of the present invention, the guy support includes two poles between which the winch may be positioned.
A telescopic crane according to the present invention may be further complemented by a fixed or luffing fly jib in the form of a latticed mast. Guy supports in accordance of the present invention may also be mounted to this type of jib.
A lateral guying is especially effective when the crane is provided with a measuring device, e.g. a load cell, for detecting a lateral deformation of the boom structure. When the deformation exceeds a predetermined admissible value, the tension member connected to the guying is activated for tautening the guying. The extent of lateral deformation can be registered directly or indirectly via crane parameters, for example, the rope tension, the rope length and the rope extension. However, forces acting upon the boom structure may be used for determination the degree of lateral deformation, such as side winds, exposure to sunlight and temperature of the boom structure.